Dioxazine compounds are used in the synthesis of valuable dyes and pigments. These compounds are typically prepared by a five-stage synthesis process which involves N-alkylation of carbazole, followed by nitration, reduction, condensation and ring closure.
Pigment violet 23 is one of pigments belonging to Dioxazine class. In the recent past, it has gained significant importance due to its outstanding properties as a colorant.
Structure:

Molecular Formula: C34H22Cl2N4O2 
Molecular Weight: 589.47
CAS Registry Number: 6358-30-1
Pigment violet-23 (carbazole violet) belongs to dioxazine class, with color ranging from bluish-red to violet shade and is used in various applications such as paint, plastic, inks, coatings and the like.
Pigment violet 23 is obtained by cyclization of 2,5-di-(9-ethylcarbazol-3-ylamino)-3,6-dichloro-1,4-benzoquinone which is synthesized by reacting chloranil (tetrachloro-p-benzoquinone) with 3-amino-9-ethylcarbazole.
U.S. Pat. No. 4,345,074 discloses synthesis of Pigment violet 23 by condensing and cyclizing 3-amino-9-ethylcarbazole with excess tetrachlorobenzoquinone in an organic solvent in the presence of acid acceptors. The process particularly focuses on carrying out the condensation reaction in the presence of 0.1 to 4% of water in order to avoid fluctuation in the yield.
U.S. Pat. No. 6,476,222 discloses a process for improving the heat stability of Pigment Violet 23 by conditioning crude Pigment Violet 23. The conditioning is carried out by grinding the crude pigment in the presence of a grinding agent and an organic solvent.
WO2012001708 discloses a process for preparing dioxazine pigments such as Pigment Violet 23, which avoids the formation of by-products. The process involves cyclization of 2,5-di-(9-ethylcarbazol-3-ylamino)-3,6-dichloro-1,4-benzoquinone in the presence of air (enriched with 19-20% of oxygen).
The known prior art processes provides synthesis of carbazole-dioxazine pigment such as Pigment Violet 23. However, there is a need for synthesizing and exploring hitherto unknown variants of carbazole-dioxazine pigment in order to exploit the inherent colour strength of dioxazine chromophore with improvement in the pigmentory properties like viscosity, transparency, gloss, heat stability, color strength and durability properties relative to Pigment Violet 23.